As a young girl growing up in the Bronx, Jane Leavy was enthralled not only by Mickey Mantle's amazing ability — at his best, he was as great as any center fielder in the history of baseball — but by his blond, blue-eyed good looks, superman physique and country-boy innocence. There are players today who are just as great and graceful — Alex Rodriguez and Josh Hamilton come to mind — but even kids who thrill to their exploits on the field are probably too wise to venerate them or fall in love, the way Leavy and countless other young fans fell in love with Mantle.

Two decades later, Leavy, by then a sportswriter, spent a day interviewing Mantle in Atlantic City, where he was working as a casino greeter — a gig that got him temporarily banned from organized baseball. Mantle drank his way through the day, concluding in the hotel bar, where he thrust an unwanted hand at her before passing out.

Leavy says that Mantle lived a double life. There was sunshine Mickey, a grinning, humble, fair-haired boy who could run like the wind and hit a baseball a mile; and there was midnight Mickey, a creepy, weepy, abusive drunk who immiserated his wife, turned his sons into underage drinking buddies and treated his adoring young fans like a swarm of annoying flies. "A drunken whoremaster," sportscaster Howard Cosell once called him, and for once Cosell wasn't guilty of overstatement.

Leavy's mission in her book "The Last Boy: Mickey Mantle and the End of America's Childhood" is to explore how two such different characters managed to inhabit the same body, and she succeeds admirably. Mantle, she explains, came along four years after Jackie Robinson integrated baseball with the Dodgers and led a long list of great black baseball players into the national pastime.

The white sporting public (a.k.a. paying customers at the turnstiles) desperately wanted to be assured that there was a blond, blue-eyed kid who could out-run and out-hit these newcomers. The classic "Who's better, Mickey Mantle or Willie Mays?" argument was about more than baseball bragging rights. White America needed Mickey Mantle to be an idol, and the Yankees public relations machine, aided and abetted by a silent sporting media, delivered.

Mantle himself knew the score. Leavy recounts the winter day he walked out of a Manhattan bar dead drunk, fell face first into the gutter, looked up at a friend and said with bitter irony, "Fine place to be for America's hero."

Of course, Mantle really was a great baseball player.

Leavy tells the story of his achievements on the diamond in competent, sportswriterly prose. But she soars when she considers the human being in the uniform. A rapidly disintegrating Mantle was dominated by Sandy Koufax, the subject of Leavy's first biography, in the 1963 World Series. Trudging back from a ninth-inning strikeout, Leavy writes, Mantle was a solitary figure: "The shadow of his former self embraced him, neither trailing behind nor pointing the way forward."

Leavy also grants Mantle his personal virtues. He was a great teammate, warm to rookies (unlike his predecessor in center field, Joe DiMaggio, who snubbed Mantle in their season together) and always willing to cut his pals in on a good deal or a good time. He could be generous, delaying the announcement of his retirement to help the players association negotiate a better contract. He took care of his coldhearted mother and his dysfunctional kinfolk in Oklahoma, although he preferred to do it from a distance. And he was brave, playing through pain throughout his career (although, as Leavy points out, he had himself to blame for failing to take care of his injuries, and for drinking and drugging his body into chronic disrepair).

As his alcoholism deepened, Mantle lost himself in his own legend. "His life became a solipsistic loop of video clips and sound bites," Leavy writes. "Much of what he knew about himself was what he was told he had once said."

Still, despite what Leavy knows about the midnight Mantle, she can't despise him. She makes allowances for the "Mad Men" mores of the time (Mantle and John F. Kennedy, another necessary hero, evidently shared a drug-pushing physician called Doctor Feelgood). She quotes a staffer at the Betty Ford Clinic who diagnosed Mantle with "acquired situational narcissism," a syndrome that tends to afflict rich, famous jerks. No doubt Mantle was wounded by life. Aren't we all?

At Mantle's funeral, in 1995, Bob Costas eulogized him as "a fragile hero to whom we had an emotional attachment so strong and lasting that it defied logic." "The Last Boy" goes a long way toward deciphering that riddle. It is a tribute to her persistence, and her talent, that she captured him whole.

Chafets, whose most recent book is " Rush Limbaugh: An Army of One," also wrote "Cooperstown Confidential: Heroes, Rogues and the Inside Story of the Baseball Hall of Fame."